A multiple input multiple output (MIMO) technology has become one of key technologies in the field of wireless communications. After continuous development in recent years, the MIMO technology is increasingly applied to various wireless communications systems. With regard to a wireless broadband mobile communications system, content related to the MIMO technology has been added to the 3rd generation partnership project (3GPP) standard, and the MIMO technology will also be applied to B3G and 4G systems. In a wireless broadband access system, the MIMO technology is also used in standards such as 802.16e, 802.11n, and 802.20 that are being formulated. In the research of other wireless communications systems, such as an ultra-wideband (UWB) system and a cognitive radio (CR) system, application of the MIMO technology is considered. In a MIMO communications system, differences exist between channels in a signal processing manner, component, channel path, and connection structure, and a delay generally exists between signals on the channels. When the delay is large, asynchronism between the channels in receiving a signal causes severe intersymbol interference on the side of a receiver. Therefore, delays of the channels need to be estimated, so as to synchronize the channels.
In the prior art, a commonly used time estimation is an offline calibration method based on measurement. Before a communications system is put into use, by using a delay of one transmit or receive channel as a reference, a delay is independently measured for each transmit or receive channel by using a meter. A problem of this method is that, this offline test method cannot measure a delay that dynamically changes, and is difficult to achieve high precision.